If you have filed your 2015 tax returns and they have been accepted, when you sign onto your online account and are on the Welcome Home screen, click on My TurboTax at the top of the screen. When you are on your 2015 tax timeline, under the section for SOME THINGS YOU CAN DO, click on Amend (change) 2015 and Download your .tax file
See this TurboTax support FAQ for amending a 2015 return completed using the online editions - https://ttlc.intuit.com/questions/2693844-how-do-i-amend-my-2015-turbotax-online-return
Or if you land on the Welcome Back screen for the 2015 Timeline instead of the Welcome Home screen -
Download the tax data file that is shown in Step 1 - Download your .tax file. See screenshot.
Download the amend software from this website - https://turbotax.intuit.com/personal-taxes/cd-download/amend/ty15/
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